One or more local agencies that implement the provisions of the SGMA. For purposes of imposing fees pursuant to Chapter 8 of the SGMA (commencing with Section 10730) or taking action to enforce a groundwater sustainability plan, "groundwater sustainability agency" also means each local agency comprising the groundwater sustainability agency of the plan authorizes separate agency action.

A GSA can generally be defined as: A local agency tasked with implementing the Sustainable Groundwater Management Act (SGMA); primarily through a coordinated Groundwater Sustainability Plan (GSP).